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In addition to creating environmental threats, the leakage and entrance of chemical fertilizers into soil, which is possible in various ways, dramatically changes the physical and mechanical properties of soil. Furthermore, clay soils in the vicinity of monoammonium phosphate (MAP) contamination show substantially negative behavior, thus, improving the engineering geological factors of soil has become a huge challenge for engineers. Extensive programs such as triaxial compression test, consolidation test, compaction test, Atterberg limits, and collapse tests, in addition to X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were performed on samples containing 10%–30% MAP over 7 days, 1, and 3 months. The mentioned trend was repeated when 0.5%–3% nano A (Al2O3 in alpha phase), nano F (Fe2O3 in alpha phase), and AF in form of a nanohybrid were added to soil which had been contaminated by MAP. Gained reports demonstrated significant declines in maximum dry density, plasticity index, and shear strength of contaminated soil when compared with natural soil. Conversely, increases in liquid limit, plastic limit, consolidation settlement, as well as soil collapse index were observed. Furthermore, a decrease in the amount of minerals in the XRD results and the formation of a flocculated structure in the SEM images in MAP-contaminated soil are evident. According to microstructural analysis, adding nano A, nano F, and AF nanohybrid as an improvement phase caused remediation of the soil structure and created cementation bonds between soil particles, thereby increasing the maximum dry density and soil shear strength, and decreasing the consolidation settlement and soil collapse index. Therefore, the use of AF as an efficient additive to remediate physical and mechanical properties of soils that have been contaminated with MAP, and to decrease the geological hazards of these kinds of contamination is recommended. [ABSTRACT FROM AUTHOR]

This paper discusses the second-order reliability-based design optimization (SORBDO) of unsaturated finite slopes. An efficient search algorithm is proposed to locate the most probable slip surfaces using the Morgenstern–Price method of slices. The variability of fitting parameters of the soil water characteristic curve (SWCC) and shear strength parameters have been taken into account for evaluating the reliability of unsaturated finite slopes. Six unsaturated shear strength (USS) models are considered for the analysis of unsaturated soils. The most conservative model for the optimum design of finite slopes is recommended. Moreover, the results indicate that the mean and standard deviation of the fitting parameters of SWCC have a significant effect on the critical centers, critical slip surfaces, and reliability index of the unsaturated finite slopes. The results demonstrate a significant change in the critical centers associated with critical slip surfaces due to the change in the mean and coefficient of variation of the fitting parameters of SWCC. Statistical analysis of the experimental data shows that a positive correlation exists between fitting parameters of SWCC related to air entry value (af) and residual water content (mf). Negative correlations are found between the fitting parameters of SWCC related to air entry value (af) and slope (nf). Similarly, the SWCC fitting parameters related to residual water content (mf) and slope (nf) have negative correlations for clayey soils. It is observed that the correlated value of the reliability index is overestimated with reference to the uncorrelated value for clayey soil slopes. The proposed design charts are beneficial for engineers and practitioners for the sustainable design of unsaturated finite slopes. Overall, the developed rigorous SORBDO framework offers a more rational approach for assessing critical failure surfaces and critical centers, considering the interdependency of random variables. [ABSTRACT FROM AUTHOR]

Excavation causes disturbance to the surrounding soil, affecting the soil's mechanical properties. This study presents a case study to investigate the effect of excavation disturbance on soil properties and pile capacity via in situ tests. A series of multifunctional piezocone tests, multichannel analysis of surface wave tests, and electrical resistivity tomography tests were conducted at three sites of the Taihu tunnel region before and after excavation with different depths. The changes in soil mechanical properties and the pile capacity loss were evaluated using the test results. The results indicated that excavation disturbance decreased the cone tip resistance, sleeve friction, soil resistivity, shear wave velocity, and undrained shear strength. In contrast, the friction ratio and the effective friction angle were not affected. The average cone tip resistance of soils in the excavation disturbance zone was approximately 51%, 46%, and 62% of its initial value at Sites A, B, and C, respectively. The variation in soil properties was only observed within a limited depth below the excavation surface, which is defined as the excavation disturbance zone. The piezocone test successfully identified the depth of the excavation disturbance zone, and the disturbance zone height was approximately 0.42 times the excavation depth. In the disturbance zone, the cone tip resistance and the undrained shear strength of the soil decreased linearly from approximately 90%–0% with increasing depth. Because of excavation disturbance, the axial and lateral capacities of a pile beneath the Taihu tunnel were reduced by about 9% and 50%, respectively. [ABSTRACT FROM AUTHOR]